1. Field of the Invention
The present invention relates to magnetic sensors utilizing a tunneling effect for use in magnetic sensing apparatuses such as magnetic playback apparatuses, including hard disk drives. In particular, the invention relates to a tunneling magnetic sensor capable of providing a reduced absolute value of VCR (voltage coefficient of resistance), low RA (the product of sensor resistance, R, and sensor area, A), and a high rate of resistance change (ΔR/R) and a method for producing such a tunneling magnetic sensor.
2. Description of the Related Art
A tunneling magnetic sensor (tunneling magnetoresistive element), which utilizes a tunneling effect to cause a resistance change, includes a pinned magnetic layer, a free magnetic layer, and an insulating barrier layer (tunneling barrier layer) disposed therebetween. If the magnetization of the free magnetic layer is antiparallel to that of the pinned magnetic layer, a tunneling current flowing through the insulating barrier layer is minimized, meaning that the resistance is maximized. If the magnetization of the free magnetic layer is parallel to that of the pinned magnetic layer, the tunneling current is maximized, meaning that the resistance is minimized.
Based on this principle, a change in electrical resistance is detected as a voltage change when an external magnetic field changes the magnetization of the free magnetic layer. The tunneling magnetic sensor thus senses a leakage magnetic field from a recording medium.
Japanese Unexamined Patent Application Publication Nos. 2000-91666 (Patent Document 1) and 2000-322714 (Patent Document 2) disclose inventions related to tunneling magnetic sensors.
The inventions disclosed in Patent Documents 1 and 2 are directed to the prevention of oxidation of magnetic layers.
It has been found that the use of titanium oxide (Ti—O) for the insulating barrier layer extremely increases the absolute value of VCR, a measure of the dependence of sensor resistance on voltage change. Higher absolute values of VCR are disadvantageous because they result in larger variations in sensor resistance and decreased operating stability (unstable operation). Accordingly, an improvement for reducing the absolute value of VCR is demanded.
In addition, a high rate of resistance change (ΔR/R) should be provided within a low range of RA. High RA causes problems such as difficulty of high-speed data transmission, and a low rate of resistance change (ΔR/R) poses the difficulty of increasing output.
In the inventions disclosed in Patent Documents 1 and 2, the insulating barrier layer is formed of aluminum oxide (magnesium oxide is also disclosed in Patent Document 2), rather than being formed of titanium oxide.
Hence, the above problem associated with the use of an insulating barrier layer formed of titanium oxide is not recognized in the inventions disclosed in Patent Documents 1 and 2, which of course disclose no method for improving the above characteristics, namely, VCR, RA, and the rate of resistance change (ΔR/R).